Out of 115 named elements on Earth, 92 classify as natural elements. These elements exclude substances deriving from chemical bases, which do not break down into simpler molecules. The family of natural elements starts with hydrogen and proceeds down the period table of elements to uranium.
The natural elements numbered 1 through 92 contain similar physical properties. They classify entirely as natural, with the exception of elements 43 and 61, or technetium and promethium. These two elements have less structural stability than the natural elements. Their isotopes also express shorter half-lives than those of pure natural elements. Half-lives of these two elements cover a wide period of duration, spanning mere seconds to more than 4 million years. As with other elements on the periodic table, the natural elements exist in a particular order. Those with similar physical and chemical properties and weights exist close together on the chart. They enjoy similar characteristics, such as color, mineral composition and classification as metals or nonmetals. Like natural elements, the elements following uranium classify primarily as metals and nonmetals. A few belong to the class of metalloids, which features elements bearing characteristics of metals and nonmetals. Unlike natural elements that exist in the atmosphere, water and soil, elements beyond uranium, called transuranium particles, form from artificial sources.